This invention relates to an oxidation process using rhodium nitro complexes to transfer oxygen to organic substrates having an olefinic bond. More particularly, this invention relates to a liquid phase oxidation process using rhodium nitro complexes, in the absence of other Group VIII metals as activators, to transfer oxygen to organic substrates having an isolated olefinic bond.
Only a few rhodium nitro complexes are known. These known rhodium complexes are either polynitro rhodium complexes or thermally unstable pentammine rhodium mononitro dicationic complexes, e.g., [(NH.sub.3).sub.5 RhNO.sub.2 ].sup.2+ (Cl.sup.-).sub.2 (See for Example, M. A. Hitchman and G. L. Rowbottom, Coordination Chemistry Reviews, 1982,42, 55-122). Further, both types of these known rhodium nitro complexes are not obtainable by oxidation of the corresponding nitrosyl complexes by molecular oxygen and therefore are unsuitable for the oxidation process of the present invention.
U.S. Pat. No. 4,191,696 (B. S. Tovrog et al.) discloses a liquid phase oxidation process wherein nitro complexes of Group VIII metals such as cobalt transfer oxygen to easily oxidizable organic substrates such as triphenylphosphine. However, when the substrate is a more difficultly oxidizable compound such as a compound having an isolated olefinic bond, U.S. Pat. No. 4,191,696 discloses that it is useful to activate the olefinic compound to be oxidized by complexing the olefinic bond with a divalent palladium compound or to activate the metal nitro complex by use of a Lewis acid such as boron trifluoride etherate.
B. S. Tovrog et al. in our U.S. Pat. No. 4,322,562, that is a continuation-in-part of U.S. Pat. No. 4,191,696, discloses a cyclic or catalytic oxidation process wherein a nitro complex of a Group VIII metal such as cobalt transfers an oxygen atom from the nitro ligand to an olefinic compound complexed with a divalent palladium compound. The nitrosyl ligand of the metal nitrosyl complex, formed as a coproduct with the oxidation product of the olefinic compound, is reoxidized by molecular oxygen, in the presence of a monodentate base such as pyridine, to the nitro ligand.
M. A. Andrews et al. in J.A.C.S., Vol. 103, No. 10, 1981, pages 2894-96 disclose the catalytic air oxidation of olefins to ketones by use of a divalent palladium nitro complex, Pd(CH.sub.3 CN).sub.2 ClNO.sub.2.